The dewatering of the fiber suspension by filtration is an important process within the papermaking process. The fiber suspension is a mixture of wood or cellulose fibers, fillers, auxiliary chemical agents and mainly water. This filtration process, which is often also called sheet formation, takes place in the sheet forming part of the wet part of the papermaking machine.
To be able to produce a paper sheet as uniform as possible, it is necessary to increase the amount of water to approximately 99% within the fiber suspension immediately before sheet formation. During the sheet forming process, this proportion is reduced to approximately 80% by filtration. The paper fibers and the fillers and auxiliary agents remain as fiber mat on the papermaking screen.
While in the past dewatering took place mainly by the papermaking screen on Fourdrinier paper machines, double screen machines are being used more and more often today, preferably so-called gap formers. They are characterized in that the fiber suspension is sprayed into a gap formed by two papermaking screens. Dewatering takes place at the same time by two screens to significantly accelerate the filtration process and the production rate of the papermaking machine. At present, papermaking machines for the sanitary paper domain have speeds of more than 2,000 meters/min.
These extreme conditions in the papermaking machine require sheet forming screens designed especially for this purpose and offering high fiber support with high stability and openness. In addition, a low tendency to marking of the fabric, that is to say, high fabric uniformity, is necessary especially for the domain of graphic paper.
A fabric or papermaking screen which most satisfies these requirements is described in DE 100 30 650 C1.